I need to be able to draw a polygon in the field while the landowner is there to approve it. Is there an app that is easy to use so all of the field hands can operate it? I also need to be able to export the file to be used in the equipment used to spray.

Another option is an online tool called click2shp -- it is entirely browser-based, and it allows you to draw points, lines, and polygons on top of a Google Maps basemap, and save the features as a shapefile in a single click. It works on my iPad!